Scaling laws of electron and hole spin relaxation in indirect band gap (In,Al)As/AlAs quantum dots

TL;DR

This study examines how electron and hole spin relaxation times in (In,Al)As/AlAs quantum dots scale with magnetic field and size, revealing size-dependent power-law behaviors and underlying mechanisms.

Contribution

It introduces a comprehensive model linking quantum dot size and magnetic field to spin relaxation, highlighting a size-dependent transformation in scaling laws.

Findings

Electron spin relaxation time scales as B^{-5} in 9 nm QDs.

Heavy hole spin relaxation time scales as B^{-3} in 9 nm QDs.

Both relaxation times follow B^{-9} scaling in 16 nm QDs.

Abstract

We investigate the electron and heavy hole spin dynamics as a function of magnetic field in ensembles of indirect band gap (In,Al)As/AlAs quantum dots (QDs) with type-I band alignment. Employing a comprehensive model that accounts for both the exciton level quartet and the magnetic-field-driven redistribution of excitons between these states via spin relaxation processes, we extract the electron ($\tau_{se}$) and heavy hole ($\tau_{sh}$) spin relaxation times as a function of magnetic field for QDs of varying sizes. Our analysis reveals that both $\tau_{se}(B)$ and $\tau_{sh}(B)$ exhibit power-law scaling behavior, yet the scaling exponents for electrons and heavy holes show markedly different evolution with QD size. For QDs with a diameter of about 9 nm, we find $\tau_{se}(B)\propto B^{-5}$ and $\tau_{sh}(B)\propto B^{-3}$. Remarkably, increasing the QD diameter to about 16 nm results in a drastic change of the scaling laws, with both $\tau_{se}(B)$ and $\tau_{sh}(B)$ following a $\propto B^{-9}$ dependence. We discuss the underlying mechanisms responsible for this size-dependent transformation of the magnetic field scaling behavior of carrier spin relaxation.